如果变量不存在替换为 0答案

【问题标题】：If Variable doesn't exist replace with 0如果变量不存在替换为 0
【发布时间】：2018-12-01 13:45:58
【问题描述】：

我正在使用屏幕抓取工具来提取数据并输出到 CSV。除非会话变量不存在，否则它可以完美运行。我想改变我的代码说，如果这个变量不存在，用值 0 替换。

例如如果 Session.getVariable "Figure2" 不存在，则使用值 0。

session.log( "Writing data to a file." ); 

out = new FileWriter( "C:/Users/Documents/Live/data.CSV" );
out.write ("User, Figure 1,Figure 2, Figure 3, Figure 4 ");
out.write ("\n");
out.write ( "User" ) ;
out.write (",");
out.write ( session.getVariable( "Figure1" ) );
out.write (",");
out.write ( session.getVariable( "Figure2" ) );
out.write (",");
out.write ( session.getVariable( "Figure3" ) );
out.write (",");
out.write ( session.getVariable( "Figure4" ) );
out.close();

session.log( "Writing data to a file." );

【问题讨论】：

标签： java screen-scraping

【解决方案1】：

您可以使用包含此逻辑的简单方法包装变量提取：

private static String variableOrZero(String variable) {
    String retVal = session.getVaraible(variable);
    if (retVal == null) {
        retVal = "0";
    }
    return retVal;
}

然后在你的代码中使用它：

out = new FileWriter( "C:/Users/Documents/Live/data.CSV" );
out.write ("User, Figure 1,Figure 2, Figure 3, Figure 4 ");
out.write ("\n");
out.write ( "User" ) ;
out.write (",");
out.write ( variableOrZero( "Figure1" ) );
out.write (",");
out.write ( variableOrZero( "Figure2" ) );
out.write (",");
out.write ( variableOrZero( "Figure3" ) );
out.write (",");
out.write ( variableOrZero( "Figure4" ) );
out.close();

【讨论】：

如果使用 Java 8 或更高版本，也可以使用java.util.Optional 完成，例如像这样optional.ofNullable(session.getVariable(variable)).orElse("0");

【解决方案2】：

我的解决方案是使用三元运算符Another stackoverflow link for ternary operator discussion

session.log( "Writing data to a file." ); 

out = new FileWriter( "C:/Users/Documents/Live/data.CSV" );
out.write ("User, Figure 1,Figure 2, Figure 3, Figure 4 ");
out.write ("\n");
out.write ( "User" ) ;
out.write (",");
out.write ( session.getVariable( "Figure1" )==null ? 0 :session.getVariable( "Figure1" ));
out.write (",");
out.write ( session.getVariable( "Figure2" )==null?0:session.getVariable("Figure2") );
out.write (",");
out.write ( session.getVariable( "Figure3" ) );
out.write (",");
out.write ( session.getVariable( "Figure4" ) );
out.close();

session.log( "Writing data to a file." );

【讨论】：

【解决方案3】：

我不知道你的会话类型。所以我猜 session.getVariable() 可能返回 null。如果你运行这段代码：

import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {
        Integer integer = null;
        FileWriter out = new FileWriter( "data.CSV" );
        out.write(integer);
    }
}

程序将抛出 NullPointerException。

Java8 Optional类是一个可以保存空值的容器。我们可以用它来检查一个Integer对象是否为空。另一个错误是 write 方法是向 Stream 中写入一个字节。您需要 PrintWriter 和 print 方法才能将 int 直接写入文件。

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Optional;

public class Main {
    public static void main(String[] args) throws IOException {
        Integer a = null;
        Integer b = 1;
        FileWriter out = new FileWriter( "data.CSV" );
        PrintWriter printWriter = new PrintWriter(out);
        Optional<Integer> oa = Optional.ofNullable(a);
        Optional<Integer> ob = Optional.ofNullable(b);
        printWriter.print(oa.orElse(0));
        printWriter.print(ob.orElse(0));
        out.close();
        printWriter.close();
    }
}

【讨论】：